FAULT TYPE SELECTION SYSTEM FOR IDENTIFYING FAULTS IN AN ELECTRIC POWER SYSTEM

摘要

The fault identification system includes a first logiccircuit which is responsive to conventional protective elementswhich recognize the presence of low resistance single line-to-groundfaults for the A, B and C phases on a power transmission line. Thefirst logic circuit includes a portion thereof for recognizing andproviding an output indication of single line-to-ground faults,faults involving two phases and three-phase faults, in response tothe occurrence of different combinations of outputs from theprotective elements. A calculation circuit, when enabled, is usedto determine the angular difference between the total zero sequencecurrent and the total negative sequence current for high resistancefaults when the protective elements themselves cannot identify faultconditions. The angular difference is in one of three pre-selectedangular sectors. An angular difference in the first sectorindicates an A phase-to-ground fault or a BC phase-to-phase toground fau an angular difference in the second sector indicates aB phase-to-ground fault or a C phase-to-phase to ground fau and asignal in the third sector indicates a C phase-to-ground fault or anAB phase-to-phase to ground fault. A processor is used to determinewhich of the two possible for each angle determination is theactual fault type. An output indication of the actual fault type isthen provided.